Some bacterial toxins are produced only when the bacteria are infected with viruses. The ultimate objective of this research is to understand how toxin production is controlled in virus-infected cells. This broad objective can be initially studied in cells infected with toxinogenic Corynebacteriophage. The immediate objectives are 1) to determine the component of dipththeria toxin which is active in controlling bacterial protein synthesis and to study its specificity and mechanism of action; 2) to determine the role of toxin or toxin fragmnts as viral structural proteins; 3) to study the iron-induced toxin "inhibitory protein"; 4) to determine how strain variation in toxin production affects phage biosynthesis. The rate of production and final yields of toxin and toxin fragments will be quantitated in different strains of C. diphpheriae infected with a hypervirulent toxinogenic phage and correlated with the yields of total and infectious phage particles produced.